The present invention relates to a power transmission including one or more speed ratio modules each capable of operating in either a direct or reduction drive mode. The invention preferably contemplates the power transmission as having a modular construction wherein each speed ratio module includes a portion of the housing for the entire power transmission. The invention also particularly contemplates a unique friction device which is self-energizing to provide a selective coupling between relatively rotatable elements such as may be found in a power transmission of the type referred to above.
In the past, power transmissions have usually been designed in contemplation of a particular application. Accordingly, for a relatively broad line of vehicles or machines there may arise a need for a correspondingly wide variety of power transmissions. Generally, the need for efficient operation of a power transmission within each of the vehicles or machines has dictated the production of a generally unique power transmission for each application. This in turn has led to the need for manufacturing and stocking a large variety of parts for the various power transmissions.
It is also noted that power transmissions of the type contemplated by the present invention have generally required at least a direct drive clutch or brake and a reduction drive clutch or brake in combination with each planetary gear set in the power train. Complex mechanisms are commonly required for synchronizing operation of the various gear trains of the power transmission and particularly for precisely timing operation of the large number of clutches or brakes associated with the various speed ratio gear sets within the power transmission. The need for such mechanically complex control systems has also resulted in a substantial expense for manufacture and maintenance of the power transmission.
It has also been known in the past to employ self-energizing friction devices within such power transmissions for selectively coupling relatively rotatable shafts or elements. Cam and roller or sprague-type overrunning devices, for example, are often employed for this purpose in power transmissions. However, such devices have certain limitations. For example, they generally are self-energizing only in one direction of relative rotation. Thus, they may be employed to transmit drive torque from an input shaft to an output shaft while not being capable of transmitting coast torque from the output shaft to the input shaft.
A one-way, self-energizing friction device of the type referred to immediately above may be seen in U.S. Pat. No. 2,939,343. Additional examples of overrunning devices which are self-actuating in only one direction of relative rotation may be seen in U.S. Pat. Nos. 3,567,000 and 3,730,314, assigned to the assignee of the present invention.
It is particularly contemplated within the present invention to provide a power transmission speed ratio module which may be assembled to form a variety of power transmissions suited for different machine or vehicle applications. Such power transmissions normally include an input module such as a torque converter or slipping clutch followed by one or more speed ratio modules according to the present invention and a suitable output module. The present invention even more particularly contemplates use of such modules to form automatically controlled power shift transmissions adapted for either on-highway or off-highway vehicles. Within such applications, the power shift transmissions serve to extend the working speed and torque range of any selected prime mover such as a piston engine, rotary combustion engine, gas turbine or electric motor, for example.
The primary purpose of the present modular concept for power transmissions is the reduction of manufacturing and service costs while maintaining reliability of operation. The use of identical speed ratio modules or a selected series of such modules having different reduction ratios would reduce the number of parts required in power transmissions for a variety of applications. This in turn would permit volume production of the transmission parts and the use of automated production facilities.
As noted above, the present invention also particularly contemplates numerous specific features which may be employed within a modular power transmission of the type discussed above as well as in other applications. Such specific features include, but are not limited to, the self-energizing clutch or friction device referred to above as well as a common control assembly employed to condition both the direct drive clutch and the reduction drive clutch to selectively establish different speed ratios within each module.
The term "friction device" is employed below and particularly within the claims with the intention of encompassing both clutches and brakes, for example. The particular device as illustrated in the drawings outlined below and described within the specification may arguably be considered a brake, since one portion of the device is fixed against rotation. In particular, the friction device serves to condition the transmission or a modular portion thereof for the transmission of torque in different modes depending upon operating conditions and associated control apparatus.